1. Field of the Invention
This invention relates generally to flow measurement of particulate streams and in particular to a Dopplar flow meter and method for flow measurement of particulate streams.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Flow measurement of particulate streams such as wet cakes, grains, cereals, dry powders, minerals, pharmaceuticals, dairy powders, chemicals, spices, snack foods, cement, resins, plastics, fibrous materials, and others is critical to the operation and optimization of a given process. A non-contact flow meter is of great importance since measurements are obtained without interfering with the flow of product through the process transfer line. For flow measurement of some products through transfer lines, this is critical since any obstruction in the line can cause buildup and eventual pluggage. In addition, no degradation of the material occurs since the flow is unobstructed. Also, the integrity of the process is maintained with a non-contact flow meter. For example, with food and pharmaceutical manufacturing, a truly non-contact solids flow meter obtains measurements without any contamination of the process since, being a non-contact device, the integrity of the process is never compromised. This factor is important when considering food, pharmaceutical, mineral, and chemical manufacturing.
Some typical applications for flow/quantity measurements are: feed to dryers, discharge from dryers, feed to milling operations, flow to mixers, flow from dust collectors, flow from conveyors, loading/unloading of railcars, loading/unloading of trucks, loading/unloading of barges, flow of grains through ducts, cement loading/unloading, flow of plastic granules, flow from cyclones, flow in pneumatic transfer lines, loading/unloading of silos, and feed to reactors to mention a few applications.
In U.S. Pat. No. 4,091,385, a Doppler radar flow meter is disclosed in which the flow meter comprises a radar transmitter and receiver that respectively radiates radio waves at a predetermined microwave frequency at least partially through a fluid and receive at least a portion of the radio waves backscattered by at least some of the particulate matter in the path of the radiated radio waves. A signal processor connected to the receiver produces a signal related to the Doppler's shift in frequency between the backscattered radio waves and the radiated radio waves and, thus, the frequency is related to the velocity of flow of the particulate matter being measured. In particular in this case, the flow meter is used for velocity of flow of fluids such as blood in conduits such as blood vessels.
U.S. Pat. No. 5,550,537 discloses an apparatus for measuring mass flow rate of a moving medium using Doppler radar. The patent discloses a non-intrusive mass flow rate meter that includes a transceiver that transmits an electromagnetic signal of known frequency and power to illuminate a portion of moving material. The transceiver detects the magnitude and the Doppler shift of the electromagnetic signal that is reflected by material moving along the process flow as it passes through the electromagnetic field established by the signal. The transceiver then combines the magnitude of the reflected electromagnetic signal along with the Doppler shift between the frequency of the transmitted and reflected electromagnetic signals to generate an output signal related to the mass flow rate of the material. The problem with the U.S. Pat. No. 5,550,537 patent is that only a portion of the moving material is illuminated. This creates errors in the mass flow rate and thus in the quantity of material that is passing through the conduit.